Sedimentary ores form through sedimentation processes. Sediments are weathered from primary rocks by physical and chemical breakdown, then transported and deposited by agents like wind and water in sedimentary basins. Through diagenesis and cementation, sediments consolidate into sedimentary rocks. These rocks form through mechanical, chemical, or biogenic processes. Economically important sedimentation processes include coalification, biogeneous shale formation, residual concentration, and mechanical concentration in placer deposits. Coal forms over millions of years as plant remains are buried and undergo heat and pressure to form carbon-rich rock.

1. Sedimentary Ore
Forming Process
By
Abdul Bari Qanit
M.Sc. Geology

2. Sedimentation
The process of settling or being deposited
as a sediment.

3. Sedimentation is a process of sediment derivation from the primary rocks
which are weathered by physical disintegration and chemical
decomposition. These sediments are transported by different geological
agents (wind, water, gravity) and deposits in a favorable place called
sedimentary Basin. After the deposition the process called diagenesis will
be consolidated and cemented the grains of the sediments resulting the
sedimentary rocks.

4. Making of Sedimentary
Rocks

5. Generally the sedimentary rocks formed in
three ways:
a) Mechanically formed Sediments :
formed by mechanical means. Such as sandstone,
conglomerate, breccia etc.

6. b) Chemically formed Sediments:
formed from materials derived by chemical
decomposition and transported by solution activity and
deposited by precipitation. Such as Limestone and Dolomite.

7. c) Biogenetic Sediments:
in certain cases the source material for
sediments will be derived from plant/tree materials.
Such as Peat and coal.

8. Economic Process in
Sedimentation
 Coalification / Petrification
 Biogeneous Shale
 Residual Concentration
 Mechanical Concentration (Placers).

9. Coal
A black rock formed from Prehistoric
plant remains, composed largely of
carbon and burned as a fuel.

10. Formation of Coal
Coal is a non-renewable energy source because it takes millions of years to form.
That means what is in the ground now is all there is and we can’t realistically make
more.
The energy in coal comes from energy that was stored in giant plants that lived
hundreds of millions of years ago in swamp forests, even before the dinosaurs! When
these giant plants and ferns died, they formed layers at the bottom of the swamps.
Water and dirt began to pile up on top of the dead plant remains. Over thousands of
years pressure and heat would build up on top of the plant remains, undergoing
chemical and physical changes and pushing out the oxygen, turning these remains
into what we call coal.

11. Coal Formation

12. Biogeneous Shale
It’s the most important source rock for generation of oil and gas in
different sedimentary basin all over the world.

13. Residual Concentration
Residual concentration results in the accumulation of valuable minerals
when undesired constituents of rocks or mineral deposits are removed
during weathering.
Usually a “Residue” is a substance left.
Valuable deposits of iron ore, manganese, bauxite, clays, nickel,
phosphate, kyanite, barite, ochre, tin, gold and other substances occur
as residual concentrations.

15. Residual deposits form in two ways:
1) the residue is simply an accumulation of a mineral that
has not changed during the process e.g. iron oxides in banded
iron formations.

16. 2) the valuable mineral first comes into existence as a result of
weathering processes, and then persists and accumulates e.g. the
feldspars of a syenite decomposes upon weathering to form bauxite,
which persists at the surface while other constituents are removed in
solution.

17. Mechanical Concentration
Mechanical concentration is the natural gravity
separation of heavy from light minerals by means of
moving water or wind. And the resulting deposits are
called “placer deposits”.

19. Type of Placer Deposits
a. Eluvial placer (where the agent for deposition is gravity).
b. Stream Placer (where the agent for deposition is running water).
c. Marine Placer (where the agent for deposition is wave action).
d. Eolian placer (where the agent for deposition is wind).

21. The End